The present invention concerns a combustion furnace for solid fuel, including combustable fuel, as stated in the introductory part of claim 1.
So called xe2x80x9cRefined Derived Fuelxe2x80x9d, RDF, is the result of sorting out non-combustible elements from household waste, etc. RDF can be mixed with cortex and wood chips in order to acheive a better calorific value. This fuel is burned in special furnaces to extract the optimum amount of energy while keeping pollution as low as possible. Such furnaces should also be able to process other solid materials, such as all kinds of biomass, mud, and certain types of hazardous waste.
In principle, a furnace for combustion of RDF operates in a manner where the fuel is supplied at a grate which is located over a primary air chamber, the chamber often being divided in sections. The combustion furnace is divided into a primary chamber and a secondary chamber, where the fuel is burned in two steps.
A disadvantages with known grate furnaces of this type is that it is difficult to acheive an optimum combustion, both for utilization of energy and reduction of pollution. This is substantially due to the furnaces not being flexible, and not including control options for adjustment of fuel of different consistency and content.
For a large part, this is solved through a furnace as described by NO-patent No. 176 455. Here the combustion chamber is separated into a primary and secondary combustion chamber, which is at least partly separated by a dividing plate. Furthermore, under the grate is situated an air supply divided into a certain number of zones which are individually controllable and have a supply of air and recirculated fume gas, preferably with a high temperature. However, it is still not possible to regulate the supply of fuel in a flexible way, for optimum utilazion of the furnace. In order to achieve an optimum combustion, it is also important that the supply of primary air to the grate is distributed as evenly as possible.
Combustion furnaces for waste, where the fuel is supplied to a grate situated above a primary air chamber are known for example from SE Patent Application No. 9301253-2 and SE Patent No. 501 226.
SE-9301253-2 discloses a simple rod feeder for transferring fuel to a primary air chamber. The disadvantage with such a rod feeder is that a risk exists that the fuel only will be lead back and forth in a kind of pendulum movement, giving an uneven distribution.
SE-501 226 also describes a simple rod feeder but has, in addition, counter scrapes which are fixed to the grate. This furnace achieves a transfer of the fuel which to a certain degree is more effective. However, it is difficult to achieve a totally even distribution of the fuel along the grate, as clusters of fuel will form in the vicinity of the stationary counter scrapes.
Furthermore, SE-501 226 discloses primary air supply from below through channels equipped with holes. However, this will cause the combustion to be uneven and most intensive in the area where the air goes into the grate.
It is thus an object with present invention to provide a device of the above mentioned kind where both the fuel and air for combustion are supplied and distributed evenly along the grate, for an optimum combustion.
The object of the invention is achieved with a combustion furnace having features as stated in the characterizing part of claim 1. Further features are apparent from the accompanying dependent claims.